1. Field of the Invention
The present invention relates to an imaging apparatus, and, more particularly, to a directionally dependent carrier isolator for an imaging apparatus.
2. Description of the Related Art
During ink jet printing, a printhead, mounted in a printhead carrier, is moved across the print medium in a reciprocating manner in a main scan direction by a carrier drive mechanism, which may include a carrier drive belt, pulleys, and a motor. While the printhead is moving in the main scan direction, ink is selectively ejected from the ink jetting nozzles to form a print swath. After completing at least one print swath, the print medium is indexed a selected amount in a sub scan, i.e., paper feed, direction.
When the carrier transports the printhead across the print medium, vibrations are developed in the carrier, which in turn are transmitted to the printhead. These vibrations cause degradation of the image quality by producing a cyclic error that contributes to vertical banding, and is visible to the naked eye. One cause of such printhead vibration is torque ripple developed in the motor used to drive the printhead carrier back and forth across the print medium. The torque ripple sets up vibratory modes in the carrier drive belt, which transfers the vibratory energy to the printhead carrier. In addition, the carrier system has a fixed frequency natural mode which produces a fluctuation in the force driving the printhead carrier, also yielding vertical banding.
Schemes for reducing such registration error have been attempted, for example, by the use of springs. However, springs alone may not provide sufficient damping to adequately absorb or isolate the offending frequency. In addition, damper inserts have been utilized, but these inserts may not provide sufficient damping at the low frequencies associated with carrier drive torque ripple. Also, some of these schemes may not provide sufficient rigidity, thereby affecting carrier drive control system response.
None of the prior systems, however, are designed to account for variations in the vibrations based on the direction of travel of the printhead carrier. For example, in one common carrier drive configuration, the carrier is transported in one direction by a direct pulling of the carrier by the carrier motor pulley, whereas to transport the carrier in the opposite direction, the carrier motor pulley indirectly pulls the carrier via an idler pulley. Thus, the mechanism for transporting the carrier has different drive characteristics depending on the direction of carrier travel, and accordingly, has differing vibration characteristics depending on the direction of carrier travel.
What is needed in the art is a device that provides directionally dependent damping of vibrations in a printhead carrier system, including its drive mechanism.